In large industrial machines such as mining and hauling trucks, it is not possible for a human operator to manually generate enough force to effectively brake or steer the machine. As such, most large trucks employ hydraulic power brakes and hydraulic power steering. These power systems direct a flow of high pressure hydraulic fluid to the machine's braking or steering actuators to effectuate the braking and steering commands given by the operator.
While a hydraulic pump may be able to supply the required flow in smaller machines, larger machines require the use of hydraulic accumulators to ensure adequate flow for braking and steering operations. A hydraulic accumulator is a device that accepts a certain volume of hydraulic fluid under pressure, and that may later release the pressurized hydraulic fluid into the machine hydraulic circuit (or brake or steering hydraulic circuit) when flow is required. In essence, an accumulator stores the output of the hydraulic pump so that the instantaneous available hydraulic flow at a later time is able to transiently exceed the output of the hydraulic pump.
There are many kinds of hydraulic accumulators, but a primary type in use today is the gas precharged hydraulic accumulator. The gas precharged hydraulic accumulator includes a vessel having therein a piston. The piston separates the inlet end of the vessel from the enclosed remainder of the vessel. The enclosed remainder of the vessel is precharged by a charge of high pressure gas, such that if there is no hydraulic pressure at the inlet, then the piston is close to the inlet and the gas is in a partially expanded state. Similarly, if there is high pressure at the inlet, then the piston is forced into the vessel, compressing the gas precharge and storing energy.
One problem with gas precharged hydraulic accumulators is that the gas precharge may leak, slowly or rapidly, rendering the accumulator ineffective for supplying peak hydraulic flow demands. This in turn may affect braking and steering, and so it is desirable to detect such a condition. In the past, it was known to periodically measure accumulator pressure to determine whether a leak had occurred. For example, U.S. Pat. No. 3,662,333 (“Hydraulic Accumulator Charge Detector and Indicating System”), discloses a technique for determining if an accumulator charge is low using repeated readings of a pressure sensitive transistor reflecting the pressure in the accumulator. In particular, when the circuit is not being used, the pressure sensitive transistor reading is stored or memorized. At a later time, if the pressure in the accumulator has dropped a predetermined amount below the stored pressure, a warning light is activated.
While such techniques may, averaged over time, provide a trend that evidences a leak, it will be appreciated that the use of the hydraulic system between readings could actually leave a leaking accumulator in a higher pressure state momentarily. This and other problems preclude the system of the U.S. Pat. No. 3,662,333 from effectively providing a real time indication of accumulator charge status.
The present disclosure is directed to a system that addresses one or more of the problems set forth above. However, it should be appreciated that the solution of any particular problem is not a limitation on the scope of this disclosure nor of the attached claims except to the extent expressly noted. Additionally, the inclusion of any problem or solution in this Background section is not an indication that the problem or solution represents known prior art except as otherwise expressly noted.